1. Field of the Invention
The present invention generally relates to an industrial sewing machine and, more particularly, to an automatic fabric guide mechanism in a sewing machine for positioning and guiding a fabric to be sewed relative to the stitching needle so that the resultant stitching can extend substantially parallel to, and is hence kept spaced a predetermined distance from, one edge of the fabric regardless of whether such edge of the fabric extends straight or curved.
2. Description of the Prior Art
The automatic fabric guide mechanism of the type referred to above is well known in the art and is utilized to avoid any possible arbitrary swing of the fabric being stitched relative to the intended stitching line set up on the fabric. In the automated garment making industry, needle-workers attendant to the sewing machines seldom lay their hands on the fabric to let the latter to be fed under the stitching needle. This is particularly true where the intended stitching line extends substantially straight or substantially parallel to one edge of the fabric where such edge of the fabric is intended to be hemmed or felled, as the fabric guide mechanism referred to above works in cooperation with the feed dog against which the fabric is pressed by means of the presser foot.
Japanese patent publication No. 39-7688, published May 16, 1964, discloses a fabric guide mechanism in a sewing machine, which mechanism comprises a photoelectric detector system in combination with a unique presser foot device. The photoelectic detector system comprises a common light source and first and second light sensors. The first light sensor is positioned laterally of and spaced a predetermined distance from the feed dog for detecting the presence or absence of one lateral edge of the fabric, and the second light sensor is positioned frontwardly of the needle hole with respect to the direction of feed of the fabric and generally in alignment with the direction of such feed for detecting the presence or absence of the fabric to be placed on the needle plate.
The presser foot device disclosed therein comprises a generally L-shaped bar having short and long bar sections contiguous to each other, a free end of said long bar section opposite to the short bar section being coupled to a machine framework for pivotal movement in a vertical plane parallel to the direction of movement of the stitching needle and also in a horizontal plane perpendicular to the vertical plane. The presser foot device also comprises a main presser foot secured to a generally intermediate portion of the long bar section and an auxiliary presser piece secured to a free end of the short bar section, said auxiliary presser piece being engaged with a motor-driven roller through the fabric.
According to the above-mentioned publication, assuming that the second sensor detects the presence of the fabric to be stitched, a reversible drive motor drivingly coupled with the roller is held a position ready to be operated. The first sensor, which presumably comprises a plurality of phototransistors or Cds sensor elements as the publication describes the first sensor having a `center line` extending parallel to the direction of feed of the fabric, generates one of positive-going and negative-going signals when one lateral edge of the fabric being stitched deviates in a corresponding one of opposite directions laterally of the center line of the first sensor. The signal, either positive-going or negative-going, from the first sensor is utilized to drive the reversible drive motor so that the roller can be rotated in one of the opposite directions, depending on the state of the signal from the first sensor, to displace the fabric in cooperation with the auxiliary presser piece in a direction generally perpendicular to the direction of feed of the fabric thereby to keep the lateral edge of the fabric in alignment with the center line of the first sensor.
Japanese patent publication No. 58-48199, which was first laid open to public inspection on Sept. 3, 1977, under publication No. 52-105048, discloses an improvement over the fabric guide mechanism of the first mentioned Japanese publication. According to this second mentioned Japanese publication, the fabric guide mechanism is mounted on a flat bed of the sewing machine at a position laterally rightwards of the stitching needle and comprises a generally U-shaped stopper laid horizontally so as to open towards the stitching needle for restricting any possible rightward displacement of the lateral edge of the fabric, a motor-driven geared or friction wheel carried through a bevel gear system by a drive transmitting shaft rotatably housed within a tubular arm and terminating in driving connection with a drive motor at the opposite end of the tubular arm, a positioning system including a pneumatic cylinder for selectively lowering and raising the motor-driven wheel relative to a portion of the fabric adjacent the lateral edge thereof, and a detector system for detecting the displacement of the lateral edge of the fabric in a leftward direction towards the stitching needle and away from the stopper.
The system of the second mentioned publication is such that, only when the lateral edge of the fabric being stitched is displaced in such a direction that it may escape from the stopper, that is, the leftward direction, is the geared or friction wheel then lowered by the pneumatic cylinder to engage that lateral edge portion of the fabric and draw the fabric rightwards to move the intended stitching line into alignment with the stitching needle.
The prior art fabric guide mechanism according to any one of the previously mentioned Japanese publications has been found to have a problem in that, where the fabric to be stitched is very flexible and pliable, the fabric tends to be sewed in such a stretched fashion that the resultant stitching may bring about a series of gathers in cloth not called for. Accordingly, as disclosed in Japanese patent application No. 63-248490, filed in Japan on Sept. 30, 1988, (which has not yet been published as of the priority date of the instant application), the inventors of the present invention have previously devised an automatic fabric guide mechanism in the sewing machine which comprises, in addition to a detecting system for detecting any possible swing of the lateral edge of the fabric being sewed, at least one friction roller engageable with the needle plate through the fabric and drivingly coupled with a stepper motor mounted on a machine bench with a drive shaft extending parallel to the needle plate in a direction generally perpendicular to the direction of movement of the stitching needle. The friction roller is rotatable in a direction corresponding to the direction of feed of the fabric past a stitching position, the peripheral velocity of which is controlled by an output signal from the detecting system depending on the direction in which the lateral edge of the fabric swings during the feed thereof past the stitching position.
It has, however, been found that, in order for the stitching to be formed on the fabric substantially exactly in alignment with the intended stitching line spaced a predetermined distance inwardly from the lateral edge of the fabric, the fabric guide mechanism according to the above-mentioned prior invention requires the use of a complicated and expensive electric or electronic control system effective to control the peripheral velocity of the friction roller in dependence on the speed of feed of the fabric past the stitching position. In addition, the use of the stepper motor for driving the friction roller tends to render the sewing machine as a whole to be expensive to manufacture.